Binary Liquid Crystalline Mixtures Research Articles

Ferroelectric Liquid-Crystalline Binary Mixtures Based on Achiral and Chiral Trifluoromethylphenylterthiophenes

This paper presents a new family of ferroelectric smectic liquid-crystalline binary mixtures composed of achiral and chiral trifluoromethylphenylterthiophenes. The chiral symmetry breaking of the ferroelectric smectic phases can lead to chiral photovoltaic (CPV) effects, as a type of ferroelectric photovoltaic (FePV) effect, which is caused by the internal electric field originating from the spontaneous polarization. These ferroelectric properties were examined using the Sawyer-Tower method, and the CPV effect was confirmed by measuring the steady-state photocurrent response under zero bias. We found that the remnant polarization and photocurrent density in the polarized ferroelectric phases increased nonlinearly with the increase in the content of the chiral component in the mixture. Moreover, the hole mobility evaluated by time-of-flight measurements was kept constant by varying the composition. More than 40 mol % of the chiral component was required to form the polar structure, inducing the CPV effect. Binary mixture systems are advantageous for not only optimizing liquid crystal structures and temperature ranges but also facilitating the design of materials exhibiting CPV effects.

Birefringence of binary liquid crystalline mixtures of MBBA and PPMAECOBA in TCM, interferometric assessment

The mutual influence of two mesogenic components, namely a nematic liquid crystal N-(p-methoxy-bezylidene)-butylaniline (MBBA) and a lyotropic liquid crystal poly-(phenyl-methacrylic) ester of cetyloxybenzoic acid (PPMAECOBA) in tetra-chloromethane (TCM) is studied in this paper. The ordinary and extraordinary refractive indices of the mixtures, nematic liquid crystal and lyotropic liquid crystal were measured at 589.3 nm with a Rayleigh interferometer and some electro-optical parameters were computed. The main refractive indices, the birefringence, the main normalized polarizabilities and their difference are dependent on the mixture volumetric concentrations, proving the existence of the collective orientational interactions between the two types of liquid crystals.

Mesomorphic, electro-optic and structural properties of binary liquid crystalline mixtures with ferroelectric and antiferroelectric liquid crystalline behaviour

ABSTRACT Two new binary liquid crystalline mixtures composed from the chiral liquid crystalline materials with partially fluorinated non-chiral chain and without lateral substitution at the molecular core have been designed and investigated by polarisation optical microscopy, differential scanning calorimetry, broad-band dielectric spectroscopy, and X-ray techniques. Both mixtures possess the paraelectric orthogonal smectic A*, the tilted ferroelectric smectic C* and the antiferroelectric smectic CA* phases over a reasonably broad temperature range. The gained results reveal a considerable improvement of (i) the broadness of the mesophases temperature range of the ferroelectric and antiferroelectric phases (up to 130 K breadth) and (ii) electro-optical properties, namely the spontaneous polarisation (up to 200 nC/cm2) and tilt angle (higher than 40o), with respect to that of the original pure compounds.

Influence of underlying local organisations in typical nematic phase of 6CHBT and induced nematic phase of bicomponent liquid crystalline systems 4DBT–12CB – a Fast Field Cycling NMR investigation

ABSTRACTVariable-temperature proton magnetic relaxation dispersion (PMRD) profiles are collected in the induced nematic phases of the binary liquid crystalline mixtures composed of smectic mesogens: 5-butyl-2-(4-isothiocyanatophenyl)-1,3-dioxane (4DBT) and 4′-dodecyl-4-cyanobiphenyl (12CB) and the low viscous nematogen 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT), with a view to assess the influence of local organisations on the power spectrum of director fluctuation modes. Two distinct compositions of the binary mixture i.e. 50 mol% of 12CB (without a smectic phase) and 70 mol% of 12CB (with a smectic phase) are used. Fast Field Cycling nuclear magnetic resonance relaxometry is employed to measure proton spin-lattice relaxation rates (R1) as a function of Larmor frequency (10 kHz–30 MHz). PMRD data analysis with the choice of a suitable model indicated nematic clusters of moderate size (~200 Å) found in the broad nematic region of 50 mol% 12CB, whose size is almost invariant with temperature. On the other hand, cybotactic clusters, i.e. local smectic organisations of relatively larger size (~2000–3000 Å), are observed near the nematic–smectic transition (T > TAN) of 70 mol% 12CB. Interestingly, the shape geometry of such local organisations accessed from PMRD analysis is weakly anisotropic near TAN, while being isotropic near TNI for 70 mol% 12CB.

Electro-optic and dielectric properties of new binary ferroelectric and antiferroelectric liquid crystalline mixtures

ABSTRACTSeveral new binary liquid crystalline mixtures have been designed and their properties were studied by complementary methods. It has been shown that even both pure components used for the mixture design possess the ferroelectric behaviour; the induced antiferroelectric smectic phase has been detected for one of the prepared mixtures. The phase diagram has been constructed and the existence of the antiferroelectric phase was confirmed by switching time and dielectric spectroscopy measurements. Some of the resulted mixtures possess very high values of the tilt angle that reaches close below 45° degrees at saturation. Values of spontaneous polarisation were found within 50–200 nC/cm2 in dependence of the mixture’s composition. Due to specific properties, the obtained mixtures might be interesting for further design of multicomponent mixtures and formulation of the advanced nanocomposite systems.

Optical studies of a binary liquid crystal mixture exhibiting induced smectic A phase

A binary liquid crystalline mixture of a monotropic polar compound 4-cyanophenyl 4′-n-pentyl benzoate (CPPB) and an enantiotropic non-polar compound 4-n-hexyl phenyl 4-n′-pentyloxy benzoate (ME5O.6) shows the presence of an induced smectic A phase in the region 0.1 ≤ xCPPB ≤ 0.82, where xCPPB is the mole fraction of CPPB. The results of texture study, density study and refractive index measurements of the eutectic mixture along with those of the pure samples are reported in this paper. The density values of the eutectic mixture are found to be much higher than that of the pure samples. The determination of order parameters of the pure samples and eutectic mixture has been carried out. In order to determine the order parameters of the samples, we have used different methods, Vuks’, Neugebauer’s, modified Vuks’ and direct extrapolation method. The results of order parameters obtained from the different approaches are compared and analysed in detail.

Electro-optic and viscoelastic properties of a ferroelectric liquid crystalline binary mixture

ABSTRACTThis study describes the properties of a binary liquid crystalline mixture composed of commercially available materials, Ce-3 (4-(n-hexyloxy phenyl)-1-(2-fuethyl butyl) biphenyl-4-carboxylate) and Ce-8 (4-(2-methylbutyl) phenyl-4-n-octylbiphenyl-4-carboxylate), in a weight ratio of 50:50. Both compounds show polymesomorphism and ferroelectric properties within a relatively wide temperature range. Taken separately, each compound has its advantages and disadvantages from the technical point of view. The influence of temperature on the electro-optical and viscoelastic properties of the produced binary mixture is investigated in this paper.

Elastic response and phase behavior in binary liquid crystal mixtures.

Utilizing density-of-states simulations, we perform a full mapping of the phase behavior and elastic responses of binary liquid crystalline mixtures represented by the multicomponent Lebwohl-Lasher model. Our techniques are able to characterize the complete phase diagram, including nematic-nematic phase separation predicted by mean-field theories, but previously not observed in simulations. Mapping this phase diagram permits detailed study of elastic properties across the miscible nematic region. Importantly, we observe for the first time local phase separation and disordering driven by the application of small linear perturbations near the transition temperature and more significantly through nonlinear stresses. These findings are of key importance in systems of blended nematics which contain particulate inclusions, or are otherwise confined.

Tuning the phase diagrams: the miscibility studies of multilactate liquid crystalline compounds

Design of binary and multicomponent liquid crystalline mixtures is a very powerful tool to reach the desired self-assembling properties. Beyond many advantages, this method has a distinct negativity – it is very material-consuming. While working with unique chiral materials in the research laboratory, this problem can be solved by applying miscibility study by the contact preparation method. In this work, the miscibility studies of lactic acid derivatives and non-chiral/chiral liquid crystalline molecules of different structure have been done in order to establish the phase diagrams. Special attention is focused on the ferro(antiferro)electric smectic phases.

The Effect of the Liquid-Crystalline Order on Releasing Dye Molecules from Liquid-Crystalline Nano-Emulsions

We fabricated dye-containing liquid-crystalline nano-emulsions (LCNEs) dispersed in water, and studied the controllability of releasingdye molecules from the coreof LCNEs into water. We estimated the concentration of the dye molecules held in the core of LCNEs from transmission spectrum. As a result, it was revealed that the dye molecules are released from the core of LCNEs below the characteristic release-temperature on cooling. Moreover, the depolarized static light scattering measurement was performed to estimate the Isotropic-Nematic(I-N) phase transition temperature of low molecular weight liquid crystals in the core of LCNEs. By controlling mixing ratio of binary liquid crystalline mixture, we tuned theI-N phase transition temperature. The release-temperature completely corresponds to the I-N phase transition temperature in the coreof LCNEswithin the whole mixing ratio. Thus, we confirmed that the emergence of the liquid-crystalline order in the core of LCNEs plays a principal role in releasing the dye molecules from LCNEs.

Mesomorphism and Shape-Memory Behavior of Main-Chain Liquid-Crystalline Co-Elastomers: Modulation by the Chemical Composition

The mesomorphic behavior, shape shifting, and shape-memory types of two homologous series of main-chain liquid-crystalline co-elastomers (MC-LCEs) with composition-tunable transition temperatures and mesophases structures are reported. The weakly cross-linked macromolecules were prepared in a one-step procedure by the versatile platinum-catalyzed hydrosilylation reaction between siloxane oligomers (linear spacers and netlike point molecules) and liquid-crystalline binary mixtures, composed of defined proportions of divinylic monomeric mesogens. First, the two sets of alternated, linear copolymers with disiloxane or trisiloxane chain extender, respectively, were investigated. They either exhibit both smectic C (SmC) and nematic (N) phases or a single SmC phase, the nature of which being dictated by the length of the inserted siloxane moieties, and the temperatures ranges regulated by the composition of the mesogenic mixture (mesogens ratio). As anticipated, the thermal behavior of the corresponding co-elas...

Combinatorial Approach for the Rapid Determination of Thermochromic Behavior of Binary and Ternary Cholesteric Liquid Crystalline Mixtures

A combinatorial approach was developed for the rapid determination of thermochromic behavior of a large number of binary and ternary sterol based thermochromic liquid crystalline formulations. A binary mixture containing cholesteryl oleyl carbonate and cholesteryl nonanoate, and ternary mixtures also containing a third component, either cholesteryl oleate, cholesteryl benzoate, cholesteryl 2,4-dichlorobenzoate or cholesteryl propionate, were formulated via solvent deposition into a black Teflon coated aluminum 96 well plate. The temperature of the well plate was then varied, and the color appearance of the deposited mixture in each well was recorded. This approach allowed expedient examination of the thermochromic behavior for a large range of liquid crystal formulations. The accuracy of the rapid combinatorial technique was validated on selected thermochromic liquid crystal mixture compositions by comparing well thermochromic output with that observed using UV-vis spectroscopy on material produced in gram quantities.

Preparation and study of a thermo-responsive membrane using binary liquid crystal mixtures of cholesteryl cetyl ether and cholesteryl oleyl carbonate

A facile method for the synthesis of thermotropic liquid crystalline cholesteryl cetyl ether (CCE) was carried out from cholesterol and cetyl alcohol using montmorillonite K-10 as an acid catalyst. The aim of this study was to investigate the use of liquid crystalline blends of CCE and cholesteryl oleyl carbonate (COC) with appropriate crystal to smectic phase temperature (Tc–s) just above body temperature as a temperature-modulated drug permeation system. Using 30/70 mol ratio of COC/CCE, a mixture of desirable phase transition temperature was obtained. The phase transition behavior of COC/CCE binary liquid crystalline mixture was established by differential scanning calorimetry and polarizing optical microsopy. The COC/CCE-embedded cellulose nitrate membrane was used by an in vitro drug penetration studies. Paracetamol and mesalazine were chosen as hydrophobic and hydrophilic drug models, respectively. Paracetamol permeability through the membrane was higher at temperatures above the phase transition of liquid crystal (LC) blends (39 °C) than its permeability below the phase transition temperature of liquid crystal blends (30 °C). The drug penetration through LC-embedded cellulose membrane was influenced by the pore size of the membrane and therefore the adsorbed amount of LC. There was no penetration of mesalazine through that membrane presumably, due to the differences in hydrophilicity of LC-embedded membrane and permeated drug.

Study of Binary Cholesteric Liquid Crystalline Mixtures Doped with Some Chiral Nonmesogenic Estradiol Derivatives

We investigated the influence of some estradiol derivatives on the thermal and structural properties of binary mixtures of cholesteryl enantate and cholesteryl myristate. The characterization of the mesophases was made by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. A considerable shift of the phase transition temperature I→Ch, as well as the temperature of formation of the SmA* phase was observed. Besides phase sequences and phase transition temperatures the measurements enabled the determination of some molecular parameters of the mixtures: the thickness of smectic layers and the longitudinal spacing distance in the cholesteric phase (d) and the average distance between the long axes of neighboring molecules (D).

Nuclear spin–lattice relaxation dispersion investigation of smectic order fluctuations in isotropic and nematic phases

Proton magnetic relaxation dispersion (PMRD) measurements are made with a view to investigating the influence of an underlying smectic phase, on the isotropic and nematic phases of the binary liquid crystalline mixture of 4DBT and 12CB, at two distinct concentrations, namely 50% 12CB (has no smectic phase) and 70% 12CB (retains S Ad phase of 12CB). Analyses of the data in terms of relevant molecular processes show that the influence of smectic clusters on the nematic order fluctuations persists even in the isotropic phase. Further, the molecular dynamics are qualitatively different in the respective nematic phases of the two mixtures.

Thermal analysis of binary liquid crystalline mixtures

Two series of binary mixtures composed of bent shaped and rod like molecules are reported. The first star shaped bent core molecules were synthesized and used as a component of binary mixtures. The chiral rod like compounds having commensurable length with the arms of the bent core compounds have been chosen for these mixtures. The resulted compositions show various thermotropic liquid crystalline phases that are characteristic to both types of liquid crystalline materials. In case of mixing the rod like molecules to the bent core compound the B2, B7 and induced B1 phases have been observed. While using the star-shaped bent core and chiral rod like compounds in mixture, the paraelectric smectic A, ferroelectric smectic C* and orthogonal hexatic smectic B phases were preferred. The appearing mesophases were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction methods.

A Study of a Binary Liquid-Crystalline Mixtures with the Wide Antiferroelectric Phase

Binary mixtures of fluorinated materials having broad antiferroelectric phase have been prepared. A set of phase parameters (phase transition temperatures and enthalpies, the spontaneous polarization and the tilt angle) of pure antiferroelectric components and mixtures prepared using them have been studied. Electrooptical investigations of obtained mixtures have been conducted. An influence of mole mixing ratio of two components on evolution of electrooptical switching from tristable through V-shaped to W-shaped characteristics has been observed. The thresholdless switching of a mixture with specific mixing ratio has been ascribed as the result of the formation of frustrated phase in the medium.

Atomistic Molecular Dynamics Simulation of Benzene as a Solute in a Columnar Discotic Liquid Crystal

A molecular dynamics simulation study on a binary liquid-crystalline mixture, where the solvent is the typical discogen hexakis-pentyloxy-triphenylene in its columnar state, while benzene is the solute, is reported. Both discotic and benzene molecules are modeled employing an atomistic force field. Attention has been paid to the structural and dynamic properties of benzene in this unusual environment, comparing these results with available experiments on the same or similar systems and with computer simulation data on neat liquid benzene.

Liquid crystalline binary mixtures at the air–water interface

The interaction behaviour of the binary mixtures composed of the liquid crystals 4-octyl-4′-cyanobiphenyl (8CB) and 4-pentyl-4′-cyanoterphenyl (5CT) as well as biphenyl (BP) and terphenyl (TP) at different molar ratios has been studied using Langmuir technique. The surface pressure-mean molecular area isotherms have been recorded. The miscibility of the components in Langmuir films has been determined by using the additivity rule and collapse surface pressure criterion. It has been found, that 8CB is partially miscible with BP and TP. 5CT is miscible with TP, whereas the mixtures of two liquid crystals, 8CB and 5CT reveal the phase separation over a whole range of composition.

INVESTIGATIONS ON THE DYNAMIC BEHAVIOUR AND THRESHOLD VOLTAGES OF BINARY ANTIFERROELECTRIC LIQUID-CRYSTALLINE MIXTURES

We present the results from our investigations on the dynamic behaviour and threshold voltages of two novel binary antiferroelectric liquid-crystalline mixtures comprising of different quantities of two components. The first component, (S)-TFMHPBC-11, is classed as a hard antiferroelectric material and exhibits a direct SmA* to SmCA* (paraelectric to antiferroelectric) phase transition. The second component, (S)-DAF-9, is a soft antiferroelectric material in which both ferroelectric (SmC*) and antiferroelectric (SmCA*) phases, separated by several subphases, are observed. By varying the concentration of the two components the observed apparent tilt angle vs. applied field curves of the resulting mixture, in the SmCA* phase, can be ‘tuned’ from the characteristic tristate curve to a low-hysteresis structure more characteristic for a SmC* phase, whilst maintaining low threshold voltages.